Digital Video Recorders (DVRs) are entering the market as a replacement for tape-based systems such as Video Cassette Recorders (VCR). These systems provide the functionality of allowing a consumer to create digital recordings of television broadcast content, including terrestrial open-air broadcast, Community Access TeleVision (CATV), and satellite. As with earlier tape-based systems, DVR products allow recording of television programs in their entirety for later viewing. It is also common for these products to support time delayed concurrent playback, also known as “elastic” playback or “Live-Pause” playback. Elastic playback allows users to watch television content in real-time as it is being recorded. It also supports “trick play” functions such as Rewind and Pause.
Conventional DVR products are designed to work with a single TV. There are several drawbacks to this approach. For one thing, a DVR requires costly components such as a video encoder (e.g. MPEG-2) and hard drive device (HDD). Another drawback to this approach is that a program recorded local to one TV cannot be played back on another TV. For example, consider a house where a DVR is connected to a television in the living room, and another is connected to a television in the bedroom. A user could record the program in the living room, but the recorded program will reside on the DVR in the living room and cannot be played back in the bedroom.
In contrast to local DVR products, networked DVR systems are described in the patent applications listed above and incorporated herein by reference. One challenge to implementing networked DVR products is to provide a secure mechanism to preventing unauthorized copying of digital video and audio. A content provider, for example, may wish to provide access to recent movie titles on a temporary basis. The content provider may wish to charge a fixed rate for access to this title for 24 hours, using a pricing scheme analogous to movie rental outlets such as Blockbuster and Hollywood Video. A content provider may also wish to provide unlimited access to certain content only to subscribers of that premium content. This content provider may wish to allow a user to record and playback content received from their premium channel, but may not wish to allow this user to share this content in its digital format. With access to broadband Internet connections becoming commonplace, one threat is that a user could disseminate content world-wide by uploading this content to a Web-server.
Conditional access and random access techniques have been proposed or developed. For example, Scientific Atlanta has developed a PowerKey system, and General Instruments (a Motorola company) has developed the Digicipher system. These are methods for encrypting MPEG-2 data on a digital cable TV, providing encrypted keys to that content embedded in the video data stream (ECM or Entitlement Control Message) and providing access control to those encrypted keys using Out Of Band (OOB) channel messages (EMM or Entitlement Management Messages). Neither of these conditional access methods supports persistent storage or time-shifted playing of content.
In addition to the foregoing, NDS Group, PLC has developed a system known as RASP, or Random Access to Scrambled content Process, a mechanism to insert tags in encrypted media files to aid in random access of that media content. This technology is limited to data tagging and is not, by itself, capable of handling networked personal video recording.
While a number of content protection schemes may allow secure storage of media, most, if not all, would interfere with desirable PVR functions such as fast-forward, rewind, and the ability to skip to any position in the program. For example, one approach would be to encrypt an entire MPEG-2 stream without regard to the structure of the data. During playback, the stream could be decrypted as it is decoded/decompressed. This might be adequate for standard play, but consider 15× Fast-Forward where you wish to drop all frames but MPEG-2 I-frames. In this case, one would like to be able to locate and decrypt each I-frame without reading through and decrypting the rest of the data.
Another function made difficult by this approach is random access such as skip-forward 30 seconds, or jump to a specific time-code. Without knowledge of where a restart point is, and what restart point relates to what timecode, the player would be forced to decrypt the stream and parse it.
Therefore, the need exists for a networked DVR system that allows video to be distributed to any television in the home. Further, the need exists for that networked DVR system to provide secure content protection for persistent storage of digital media while still allowing trick-play functionality.